1. Field of the Invention
The present invention relates to a method of electronically controlling the fuel injection for an internal combustion engine, and more particularly, to a method of electronically controlling the fuel injection for an internal combustion engine adapted to perform a synchronous injection that fuel is injected at a predetermined period in accordance with the crank angle and an asynchronous injection that fuel is injected in asynchronism with the crank angle in acceleration.
2. Description of the Prior Art
Hitherto, such a fuel injection method is known that a fuel injection valve is provided on each of cylinders so as to project into an intake manifold, and signals fed from various sensors are processed by means of a microcomputer to judge an engine operating condition and inject fuel in amount in accordance with the operating condition. In this fuel injection method, a synchronous injection and an asynchronous injection are effected. The synchronous injection is such that fuel is injected into all cylinders simultaneously or for each specific cylinder at a predetermined period, while the asynchronous injection is such that fuel is injected in acceleration independently of the synchronous injection. More specifically, in the synchronous injection, a basic fuel injection pulse width is calculated in accordance with the engine load (the pressure in the intake pipe or the quantity of the intake air per revolution of the engine shaft) and the engine speed, as well as corrected by employing a partial lean correction coefficient, a feedback correction coefficient and other correction coefficient determined by the cooling water temperature or the like, thereby to obtain a fuel injection pulse width and a fuel injection valve is opened to inject fuel for a period of time corresponding to the fuel injection pulse width at a predetermined crank angle. On the other hand, the asynchronous injection during acceleration is effected in order to improve the engine responsiveness and the like during acceleration. In the asynchronous injection, a linear throttle sensor is attached which outputs a voltage as a linear function with respect to the throttle opening, and fuel is injected in accordance with the rate of change of the output voltage and that of the engine load independently of the synchronous injection. Since this asynchronous injection makes it possible to correct the air-fuel ratio during a transient period in the early stage of acceleration, driveability and the exhaust emission control are improved.
In the above conventional fuel injection method, however, there is a disadvantage that in the case of acceleration from a light-load operation region, the intake-pipe pressure and the intake-air quantity exceedingly increase with a slight increase in the throttle opening, so that the air-fuel ratio during acceleration cannot be properly controlled in accordance with the acceleration state.